The production of tissue paper articles often makes use of embossing processes to obtain both technical characteristics and a decoration on the finished product. Embossing is performed with various types of device comprising at least one embossing cylinder, equipped with a plurality of projections or protuberances distributed on the surface thereof, and cooperating with a pressure roller, usually provided with a yielding surface, for example made of rubber.
A web material with one or more plies are fed between the embossing cylinder and the pressure roller, and is deformed through the effect of the pressure with which the pressure roller and the embossing cylinder are pressed against each other. Deformation, which may be accompanied by at least partial breakage of the fibers composing the material, causes the formation of projections or protuberances on the web material. Several plies or layer of web material can be embossed separately and then joined by gluing, applying a glue to the protuberances of at least one of the plies and laminating the plies between two cylinders or rollers of the device. This is referred to as embossing and laminating and embossing and laminating devices. One or more smooth plies can also be joined by gluing and lamination to one or more embossed plies.
To obtain particular aesthetic and technical-functional characteristics articles with more than three plies joined to one another are produced. Multi-ply products of this type have high levels of strength, softness and absorption power.
WO-A-9944814 describes various methods and devices for the production of embossed and laminated articles. Some of these articles have more than two plies glued to one another. In an embodiment described therein (FIG. 3) a product with three plies is obtained, which are embossed on an embossing cylinder with which two pressure rollers cooperate. Two plies are fed between a first pressure roller and the embossing cylinder, and receive a glue on the protuberances, before a third ply is laid thereon. The three plies are subsequently embossed and laminated between the same embossing cylinder and a second pressure roller.
EP-A-408248 describes a device in which various embossing or laminating operations are performed on two plies. After having joined the two plies to each other, they are fed around an embossing cylinder with which two pressure rollers cooperate.
U.S. Pat. No. 6,589,634 describes a “tip-to-tip” embossing-laminating device, wherein two embossing cylinders each cooperate with a respective pressure roller to separately emboss two plies of paper. A glue is applied to the protuberances thereof by two glue dispensers each cooperating with one of the two embossing cylinders. The glued plies are laminated in a nip defined by the two embossing cylinders, into which a third ply is fed to obtain a three-ply product.
WO-A-9708386 describes a device to produce an article with two or more plies. In this device, an embossing cylinder cooperates with a first pressure roller to emboss a first sheet composed of two plies, on the protuberances of which a glue is applied. A second sheet is embossed between a second embossing cylinder and a respective pressure roller and subsequently fed to the first embossing cylinder, resting on the glued protuberances of the first sheet.
EP-A-1338412 describes a double embossing-laminating device, comprising a first tip-to-tip embossing and laminating unit, with two embossing cylinders and respective pressure rollers, and a second embossing unit, with a pressure roller and a laminating roller cooperating with a third embossing cylinder. A respective glue dispenser is associated with each embossing and laminating unit. This complex machine is designed to produce four-ply products.
U.S. Pat. No. 6,599,614 describes a tip-to-tip embossing and laminating device, wherein two embossing cylinders each cooperate with a respective pressure roller to, emboss two plies separately. These are then laminated together, with the interposition of a third ply, in the nip between the two embossing cylinders. Glue can be applied to the protuberances of the two embossed plies.
A similar device is described in, U.S. Pat. No. 5,736,223. This known device is provided with a gluing unit associated with each of the two embossing cylinders of the tip-to-tip unit. Moreover, the third intermediate ply, which is fed into the nip between the two embossing cylinders, is embossed separately between a third embossing cylinder and a third pressure roller.
U.S. Pat. No. 6,551,691 describes a device for producing a three-ply embossed web material. A first ply is embossed between a first embossing cylinder and a first pressure roller, while a second ply is embossed between a second embossing bossing cylinder and a second pressure roller. The plies thereby embossed are joined between the second embossing cylinder and a laminating roller, after insertion therebetween of a third ply. A glue is applied to the third, that is, central ply.
U.S. Pat. No. 5,382,464 describes an embossing and laminating device to produce a four-ply material, comprising four embossing cylinders and four pressure rollers. The embossing cylinders are phased to operate tip-to-tip. Two glue dispensers are provided to apply glue to the protuberances of two of the four plies, prior to reciprocal lamination.
The devices and methods described in the above documents are often complex and difficult to set up. Moreover, often they do not offer sufficient versatility, that is, they do not allow modifications to the type of article obtained.